The United States and Japan will step up their defence cooperation to deal with the threat from nuclear-armed North Korea as tensions in East Asia remain high, officials from the two allies said on Thursday.

Stand Pearce down, NSW opposition demands

The NSW opposition has accused Premier Barry O'Farrell of "running defence" for embattled MP Greg Pearce, with Labor now threatening to take action unless the finance minister answers questions about alleged drunkenness and travel rorts.

Mr O'Farrell has assured reporters claims Mr Pearce breached ministerial travel guidelines during a private trip to Canberra are being investigated by Department of Premier and Cabinet boss Chris Eccles.

He said he still had confidence in Mr Pearce despite opposition calls for the finance minister to be sacked.

"Let's just calm down, let's wait for Mr Eccles' report and let's see what that says," Mr O'Farrell said on Tuesday.

But Opposition Leader John Robertson said the Eccles investigation needed to be broadened to examine claims Mr Pearce took multiple taxpayer-funded trips to coincide with major sporting events and was so drunk during a late-night sitting he needed help to leave parliament.

In 2012, Mr Pearce took nine taxpayer-paid weekend or public holiday trips worth almost $9000, including flights to Melbourne on the same dates as the Melbourne Cup, Australian Open and AFL grand final, according to media reports.

"Greg Pearce can front up, he can call a press conference just like this and answer all those questions about his behaviour, about the use of his ministerial travel expenses, about pecuniary interest declarations.

He said the government's integrity would be "in tatters" for as long as Mr Pearce remained on the front bench.

"No one in this state would expect to be footing the bill for a minister of the government to have weekends away interstate, regardless of why they're there," he said.

"What we've got is a minister of the crown who had to be led out of the parliament by his colleagues."

Asked if he intended to refer the allegations to the Independent Commission Against Corruption, Mr Robertson said: "We'll obviously be looking at what options are available to us if the Eccles inquiry isn't expanded ... or doesn't get to the bottom of all the questions that need to be answered."